234 UTL_TCP

Using UTL_TCP

• Overview

• Security Model

• Types

• Exceptions

• Rules and Limits

• Examples

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Overview

The UTL_TCP package provides TCP/IP client-side access functionality in PL/SQL.

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Security Model

This package is now an invoker's rights package and the invoking user will need the connect privilege granted in the access control list assigned to the remote network host to which he wants to connect.

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Types

• CONNECTION Type

• CRLF

CONNECTION Type

This is a PL/SQL record type used to represent a TCP/IP connection.

Syntax

TYPE connection IS RECORD (
    remote_host    VARCHAR2(255),
    remote_port    PLS_INTEGER,
    local_host     VARCHAR2(255),
    local_port     PLS_INTEGER,
    charset        VARCHAR2(30), 
    newline        VARCHAR2(2),
    tx_timeout     PLS_INTEGER,
    private_sd     PLS_INTEGER);

Fields

Usage Notes

The fields in a connection record are used to return information about the connection, which is often made using OPEN_CONNECTION. Changing the values of those fields has no effect on the connection. The fields private_XXXX are for implementation use only. You should not modify the values.

In the current release of the UTL_TCP package, the parameters local_host and local_port are ignored when open_connection makes a TCP/IP connection. It does not attempt to use the specified local host and port number when the connection is made. The local_host and local_port fields will not be set in the connection record returned by the function.

Time out on write operations is not supported in the current release of the UTL_TCP package.

CRLF

The character sequence carriage-return line-feed. It is the newline sequence commonly used many communication standards.

Syntax

CRLF CONSTANT VARCHAR2(2 CHAR);

Usage Notes

This package variable defines the newline character sequence commonly used in many Internet protocols. This is the default value of the newline character sequence for WRITE_LINE, specified when a connection is opened. While such protocols use <CR><LF> to denote a new line, some implementations may choose to use just line-feed to denote a new line. In such cases, users can specify a different newline character sequence when a connection is opened.

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Exceptions

The exceptions raised by the TCP/IP package are listed in Table 234-2.

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Rules and Limits

The interface provided in the package only allows connections to be initiated by the PL/SQL program. It does not allow the PL/SQL program to accept connections initiated outside the program.

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Examples

The following code example illustrates how the TCP/IP package can be used to retrieve a Web page over HTTP. It connects to a Web server listening at port 80 (standard port for HTTP) and requests the root document.

DECLARE
  c  utl_tcp.connection;  -- TCP/IP connection to the Web server
  ret_val pls_integer; 
BEGIN
  c := utl_tcp.open_connection(remote_host => 'www.acme.com',
                               remote_port =>  80,
                               charset     => 'US7ASCII');  -- open connection
  ret_val := utl_tcp.write_line(c, 'GET / HTTP/1.0');    -- send HTTP request
  ret_val := utl_tcp.write_line(c);
  BEGIN
    LOOP
      dbms_output.put_line(utl_tcp.get_line(c, TRUE));  -- read result
    END LOOP;
  EXCEPTION
    WHEN utl_tcp.end_of_input THEN
      NULL; -- end of input
  END;
  utl_tcp.close_connection(c);
END;

The following code example illustrates how the TCP/IP package can be used by an application to send e-mail (also known as email from PL/SQL). The application connects to an SMTP server at port 25 and sends a simple text message.

PROCEDURE send_mail (sender    IN VARCHAR2, 
                     recipient IN VARCHAR2, 
                   message   IN VARCHAR2) IS 
    mailhost   VARCHAR2(30) := 'mailhost.mydomain.com';
    smtp_error  EXCEPTION;
    mail_conn   utl_tcp.connection;
    PROCEDURE smtp_command(command IN VARCHAR2,
                           ok      IN VARCHAR2 DEFAULT '250') 
    IS 
        response varchar2(3);
        len pls_integer;
    BEGIN
        len := utl_tcp.write_line(mail_conn, command);
        response := substr(utl_tcp.get_line(mail_conn), 1, 3);
        IF (response <> ok) THEN
            RAISE smtp_error;
        END IF;
    END;

BEGIN
    mail_conn := utl_tcp.open_connection(remote_host => mailhost,
                                         remote_port => 25,
                                         charset     => 'US7ASCII');
    smtp_command('HELO ' || mailhost);
    smtp_command('MAIL FROM: ' || sender);
    smtp_command('RCPT TO: ' || recipient);
    smtp_command('DATA', '354');
    smtp_command(message);
    smtp_command('QUIT', '221');
    utl_tcp.close_connection(mail_conn);
EXCEPTION
    WHEN OTHERS THEN
        -- Handle the error
END;

Summary of UTL_TCP Subprograms

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AVAILABLE Function

This function determines the number of bytes available for reading from a TCP/IP connection. It is the number of bytes that can be read immediately without blocking. Determines if data is ready to be read from the connection.

Syntax

UTL_TCP.AVAILABLE (
   c        IN OUT NOCOPY connection, 
   timeout  IN PLS_INTEGER DEFAULT 0)
RETURN PLS_INTEGER;

Parameters

Return Values

The number of bytes available for reading without blocking

Usage Notes

The connection must have already been opened through a call to OPEN_CONNECTION. Users may use this API to determine if data is available to be read before calling the read API so that the program will not be blocked because data is not ready to be read from the input.

The number of bytes available for reading returned by this function may less than what is actually available. On some platforms, this function may only return 1, to indicate that some data is available. If you are concerned about the portability of your application, assume that this function returns a positive value when data is available for reading, and 0 when no data is available. This function returns a positive value when all the data at a particular connection has been read and the next read will result in the END_OF_INPUT exception.

The following example illustrates using this function in a portable manner:

DECLARE
   c   utl_tcp.connection
   data VARCHAR2(256);
   len  PLS_INTEGER;
BEGIN
   c := utl_tcp.open_connection(...);
   LOOP
      IF (utl_tcp.available(c) > 0) THEN
         len := utl_tcp.read_text(c, data, 256);
      ELSE
         ---do some other things
        . . . .
      END IF
   END LOOP;
END;

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CLOSE_ALL_CONNECTIONS Procedure

This procedure closes all open TCP/IP connections.

Syntax

UTL_TCP.CLOSE_ALL_CONNECTIONS;

Usage Notes

This call is provided to close all connections before a PL/SQL program avoid dangling connections.

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CLOSE_CONNECTION Procedure

This procedure closes an open TCP/IP connection.

Syntax

UTL_TCP.CLOSE_CONNECTION (
   c IN OUT NOCOPY connection);

Parameters

Usage Notes

Connection must have been opened by a previous call to OPEN_CONNECTION. The fields remote_host, remote_port, local_host, local_port and charset of c will be reset after the connection is closed.

An open connection must be closed explicitly. An open connection will remain open when the PL/SQL record variable that stores the connection goes out-of-scope in the PL/SQL program. Failing to close unwanted connections may result in unnecessary tying up of local and remote system resources.

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FLUSH Procedure

This procedure transmits all data in the output buffer, if a buffer is used, to the server immediately.

Syntax

UTL_TCP.FLUSH (
   c IN OUT NOCOPY connection);

Parameters

Usage Notes

The connection must have already been opened through a call to OPEN_CONNECTION.

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GET_LINE Function

This function returns the line of data read.

Syntax

UTL_TCP.GET_LINE (
   c           IN OUT NOCOPY connection,
   remove_crlf IN            BOOLEAN DEFAULT FALSE,
   peek        IN            BOOLEAN DEFAULT FALSE) 
 RETURN VARCHAR2;

Parameters

Return Values

The text line read

Usage Notes

• The connection must have already been opened through a call to OPEN_CONNECTION.

• See READ_LINE for the read time out, character set conversion, buffer size, and multibyte character issues.

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GET_LINE_NCHAR Function

This function returns the line of data read in NCHAR form.

Syntax

UTL_TCP.GET_LINE_NCHAR (
   c           IN OUT NOCOPY connection,
   remove_crlf IN            BOOLEAN DEFAULT FALSE,
   peek        IN            BOOLEAN DEFAULT FALSE) 
 RETURN NVARCHAR2;

Parameters

Return Values

The text line read

Usage Notes

• The connection must have already been opened through a call to OPEN_CONNECTION.

• See READ_LINE for the read time out, character set conversion, buffer size, and multibyte character issues.

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GET_RAW Function

This function returns the data read instead of the amount of data read.

Syntax

UTL_TCP.GET_RAW (
   c     IN OUT NOCOPY connection,
   len   IN            PLS_INTEGER DEFAULT 1,
   peek  IN            BOOLEAN     DEFAULT FALSE) 
 RETURN RAW;

Parameters

Return Values

The binary data read

Usage Notes

The connection must have already been opened through a call to OPEN_CONNECTION.

For all the get_* APIs described in this section, see the corresponding READ_* API for the read time out issue. For GET_TEXT and GET_LINE, see the corresponding READ_* API for character set conversion, buffer size, and multibyte character issues.

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GET_TEXT Function

This function returns the text data read.

Syntax

UTL_TCP.GET_TEXT (
   c    IN OUT NOCOPY connection,
   len  IN            PLS_INTEGER DEFAULT 1,
   peek IN            BOOLEAN     DEFAULT FALSE) 
 RETURN VARCHAR2;

Parameters

Return Values

The text data read

Usage Notes

The connection must have already been opened through a call to OPEN_CONNECTION.

For all the get_* APIs described in this section, see the corresponding read_* API for the read time out issue. For GET_TEXT and GET_LINE, see the corresponding READ_* API for character set conversion, buffer size, and multibyte character issues.

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GET_TEXT_NCHAR Function

This function returns the text data read in NCHAR form.

Syntax

UTL_TCP.GET_TEXT_NCHAR (
   c    IN OUT NOCOPY connection,
   len  IN            PLS_INTEGER DEFAULT 1,
   peek IN            BOOLEAN     DEFAULT FALSE) 
 RETURN NVARCHAR2;

Parameters

Return Values

The text data read

Usage Notes

The connection must have already been opened through a call to OPEN_CONNECTION.

For all the get_* APIs described in this section, see the corresponding read_* API for the read time out issue. For GET_TEXT and GET_LINE, see the corresponding READ_* API for character set conversion, buffer size, and multibyte character issues.

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OPEN_CONNECTION Function

This function opens a TCP/IP connection to a specified service.

Syntax

UTL_TCP.OPEN_CONNECTION  (
   remote_host      IN VARCHAR2,
   remote_port      IN PLS_INTEGER,
   local_host       IN VARCHAR2 DEFAULT NULL,
   local_port       IN PLS_INTEGER DEFAULT NULL,
   in_buffer_size   IN PLS_INTEGER DEFAULT NULL,
   out_buffer_size  IN PLS_INTEGER DEFAULT NULL,
   charset          IN VARCHAR2 DEFAULT NULL,
   newline          IN VARCHAR2 DEFAULT CRLF,
   tx_timeout       IN PLS_INTEGER DEFAULT NULL)
  RETURN connection;

Parameters

Return Values

A connection to the targeted TCP/IP service

Usage Notes

• Note that connections opened by this UTL_TCP package can remain open and be passed from one database call to another in a shared server configuration. However, the connection must be closed explicitly. The connection will remain open when the PL/SQL record variable that stores the connection goes out-of-scope in the PL/SQL program. Failing to close unwanted connections may result in unnecessary tying up of local and remote system resources.

• In the current release of the UTL_TCP package, the parameters local_host and local_port are ignored when open_connection makes a TCP/IP connection. It does not attempt to use the specified local host and port number when the connection is made. The local_host and local_port fields will not be set in the connection record returned by the function.

• tx_timeout is intended to govern both the read operations and the write operations. However, an implementation restriction prevents tx_timeout from governing write operations in the current release.

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READ_LINE Function

This function receives a text line from a service on an open connection. A line is terminated by a line-feed, a carriage-return or a carriage-return followed by a line-feed.

Syntax

UTL_TCP.READ_LINE (
   c           IN OUT NOCOPY connection,
   data        IN OUT NOCOPY VARCHAR2 CHARACTER SET ANY_CS,
   peek        IN            BOOLEAN DEFAULT FALSE) 
 RETURN PLS_INTEGER;

Parameters

Return Values

The number of characters of data received

Usage Notes

The connection must have already been opened through a call to OPEN_CONNECTION. This function does not return until the end-of-line have been reached, or the end of input has been reached. Text messages will be converted from the on-the-wire character set, specified when the connection was opened, to the database character set before they are returned to the caller.

If transfer time out is set when the connection is opened, this function waits for each data packet to be ready to read until time out occurs. If it occurs, this function stops reading and returns all the data read successfully. If no data is read successfully, the transfer_timeout exception is raised. The exception can be handled and the read operation can be retried later.

If a partial multibyte character is found at the end of input, this function stops reading and returns all the complete multibyte characters read successfully. If no complete character is read successfully, the partial_multibyte_char exception is raised. The exception can be handled and the bytes of that partial multibyte character can be read as binary by the READ_RAW function. If a partial multibyte character is seen in the middle of the input because the remaining bytes of the character have not arrived and read time out occurs, the transfer_timeout exception is raised instead. The exception can be handled and the read operation can be retried later.

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READ_RAW Function

This function receives binary data from a service on an open connection.

Syntax

UTL_TCP.READ_RAW (
   c     IN OUT NOCOPY connection,
   data  IN OUT NOCOPY RAW,
   len   IN            PLS_INTEGER DEFAULT 1,
   peek  IN            BOOLEAN     DEFAULT FALSE)
 RETURN PLS_INTEGER;

Parameters

Return Values

The number of bytes of data received

Usage Notes

The connection must have already been opened through a call to OPEN_CONNECTION. This function does not return until the specified number of bytes have been read, or the end of input has been reached.

If transfer time out is set when the connection is opened, this function waits for each data packet to be ready to read until time out occurs. If it occurs, this function stops reading and returns all the data read successfully. If no data is read successfully, the transfer_timeout exception is raised. The exception can be handled and the read operation can be retried later.

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READ_TEXT Function

This function receives text data from a service on an open connection.

Syntax

UTL_TCP.READ_TEXT (
   c    IN OUT NOCOPY connection,
   data IN OUT NOCOPY VARCHAR2 CHARACTER SET ANY_CS,
   len  IN            PLS_INTEGER DEFAULT 1,
   peek IN            BOOLEAN     DEFAULT FALSE) 
RETURN PLS_INTEGER;

Parameters

Return Values

The number of characters of data received

Usage Notes

The connection must have already been opened through a call to OPEN_CONNECTION. This function does not return until the specified number of characters has been read, or the end of input has been reached. Text messages will be converted from the on-the-wire character set, specified when the connection was opened, to the database character set before they are returned to the caller.

Unless explicitly overridden, the size of a VARCHAR2 buffer is specified in terms of bytes, while the parameter len refers to the maximum number of characters to be read. When the database character set is multibyte, where a single character may consist of more than 1 byte, you should ensure that the buffer can hold the maximum of characters. In general, the size of the VARCHAR2 buffer should equal the number of characters to be read, multiplied by the maximum number of bytes of a character of the database character set.

If transfer time out is set when the connection is opened, this function waits for each data packet to be ready to read until time out occurs. If it occurs, this function stops reading and returns all the data read successfully. If no data is read successfully, the transfer_timeout exception is raised. The exception can be handled and the read operation can be retried later.

If a partial multibyte character is found at the end of input, this function stops reading and returns all the complete multibyte characters read successfully. If no complete character is read successfully, the partial_multibyte_char exception is raised. The exception can be handled and the bytes of that partial multibyte character can be read as binary by the READ_RAW function. If a partial multibyte character is seen in the middle of the input because the remaining bytes of the character have not arrived and read time out occurs, the transfer_timeout exception is raised instead. The exception can be handled and the read operation can be retried later.

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WRITE_LINE Function

This function transmits a text line to a service on an open connection. The newline character sequence will be appended to the message before it is transmitted.

Syntax

UTL_TCP.WRITE_LINE (
   c    IN OUT NOCOPY connection,
   data IN            VARCHAR2 DEFAULT NULL CHARACTER SET ANY_CS) 
  RETURN PLS_INTEGER;

Parameters

Return Values

The actual number of characters of data transmitted

Usage Notes

The connection must have already been opened through a call to OPEN_CONNECTION. Text messages will be converted to the on-the-wire character set, specified when the connection was opened, before they are transmitted on the wire.

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WRITE_RAW Function

This function transmits a binary message to a service on an open connection. The function does not return until the specified number of bytes have been written.

Syntax

UTL_TCP.WRITE_RAW (
   c    IN OUT NOCOPY connection,
   data IN            RAW,
   len  IN            PLS_INTEGER DEFAULT NULL) 
 RETURN PLS_INTEGER;

Parameters

Return Values

The number of bytes of data transmitted

Usage Notes

The connection must have already been opened through a call to OPEN_CONNECTION.

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WRITE_TEXT Function

This function transmits a text message to a service on an open connection.

Syntax

UTL_TCP.WRITE_TEXT (
   c    IN OUT NOCOPY connection,
   data IN            VARCHAR2 CHARACTER SET ANY_CS,
   len  IN            PLS_INTEGER DEFAULT NULL) 
 RETURN num_chars PLS_INTEGER;

Parameters

Return Values

The actual number of characters of data transmitted

Usage Notes

The connection must have already been opened through a call to OPEN_CONNECTION. Text messages will be converted to the on-the-wire character set, specified when the connection was opened, before they are transmitted on the wire.